The invention described herein was made in the course of or under a contract or subcontract thereunder with the Department of the Air Force.
This invention relates to reflected and/or otherwise return wave systems, and more particularly, to a system for transmitting an output signal which is cross polarized with respect to an input signal.
In the past, cross polarization has been accomplished by the use of a microwave nulling network using reciprocal electromechanical phase shift elements. This is a two-port network in which an input signal is resolved into two orthogonal components. The two outputs are used to derive error signals which are applied to control mechanical phase shifting devices until one of the output ports is nulled. Use of a two-port network in which an error signal is utilized to control a phase shifter to null an error is well-known in the art. Examples are found in, for example, monopulse radar tracking circuits.
A desirable improvement in such two-port networks would be the inclusion of solid-state phase shifters in place of mechanical phase shifters. Solid-state phase shifters have improved switching speed which improves system operation. However, an obstacle in the use of solid-state phase shifters is inadequate reciprocity. In other words, while coupling a signal in a first direction from antenna to receiver, a phase shift of a first value is provided, but a phase shift of a different value is provided when transmitting a signal in the opposite direction, from a transmitter to the antenna.